The present application relates to the field of fluidic systems, and more particularly, to stirring/agitation of fluid within micro-fluidic systems.
Micro-fluidics is directed to the behavior, control and manipulation of microliter and smaller volumes of fluids. It is a multidisciplinary field bringing together physics, chemistry, engineering and biotechnology, with practical applications to the design of systems in which such small volumes of fluids will be used. Micro-fluidics has applications in the development of DNA chips, micro-propulsion, micro-thermal technologies, and lab-on-a-chip technology, among others.
The behavior of fluids at the microscale can differ from ‘macrofluidic’ behavior in that factors such as surface tension, energy dissipation, and fluid resistance start become main factors in such system. Micro-fluidics studies how these behaviors change, and how they can be worked around, or exploited for new uses. At these scales, some interesting and non-intuitive properties appear. For example, the Reynolds number, which characterizes the presence of fluid flow turbulence, is extremely low, resulting in a laminar fluid flow.
Extracting a sample fluid from a collection chamber of a fluidic system can be challenging, particularly when the collection chamber contains small amounts of fluid, such as in the range of approximately 1.5 milliliters down to 10 microliters. One type of fluidic system which holds such small amounts of fluids is a particle concentrator to which the present concepts are applicable.
Particle concentrators operate on a sample fluid containing particles of organic, inorganic, as well as other biomaterials to capture a concentrated sample, usually within a fluid channel or collection chamber. Thereafter, the concentrate sample is commonly extracted from the particle concentrator using a pipette, a syringe needle, pressure driven extraction, such as jetting, or by other appropriate mechanisms. An issue in such systems is that the particles may adhere to surfaces of the particle concentrator due to adhesive forces such as electrostatic or Van der Waals attractive forces. When this occurs, the particles which have adhered to the surfaces of the particle concentrator will not be extracted, resulting in a lower amount of the particles being obtained for investigation.
Another use of fluidic systems is for mixing together two distinct fluids, for example, to obtain a chemical reaction, heat transfer, etc. Often the two fluids do not mix rapidly enough by diffusion simply by bringing them together, resulting in an incomplete mixing of the fluids even after an extended period of time. This result may affect the outcome of the process which may have been undertaken for commercial and/or experimental reasons. In each of the above situations and others, an active rapid mixing of fluids may be desirable.
One proposal for the agitation or stirring of fluids is by the use of a bead stirrer or external ultrasonic agitation. An alternative form of agitation is by fluid-flow induced agitation accomplished by pumping a fluid in the extraction chamber back and forth by the application of an external pressure source. Examples of such ultrasonic and fluid-flow agitation are set forth in patents and applications cited within the Incorporation by Reference section of this document.